Wound field rotating machine with capacitive power transfer

ABSTRACT

An electrical rotating machine, such as a generator or motor, communicates power from a stationary location to the rotating rotor of the rotating machine via opposed pairs of capacitor plates, one plate of each pair rotating with the rotor and one plate of each pair fixed not to rotate. In one embodiment, separation between the plates of the pair is provided by a cushion of entrapped air.

BACKGROUND OF THE INVENTION

The present invention relates to wound field synchronous machines (e.g.electrical motors and generators) and in particular to a wound fieldsynchronous machine using capacitive coupling to transfer electricalpower to the rotor.

Electrical motors and generators share similar structures of amagnetically interacting stator and rotor and may be collectively termed“electrical rotating machines.” Electrical rotating machines employingpermanent magnets for the rotor are termed permanent magnet synchronousmachines (PMSM) and are popular in high-volume traction applications(e.g. motor drives for hybrid vehicles) and for compact electricalgeneration (e.g. generators used in wind turbines) because of their hightorque density and efficiency.

The permanent magnets in PMSMs typically use rare earth materials oflimited supply whose extraction and refinement may inflict detrimentaleffects on the environment. For this reason, wound field synchronousmachines (WFSM), using an electrical coil in place of the permanentmagnet on the rotor, have received renewed attention. WFSMs have lowertorque density in comparison to PMSMs but, by permitting control of therotor field directly, allow more sophisticated motor control, forexample, permitting high power factor throughout the machine operatingrange of different operating speeds and torques. The ability to controlthe rotor field also permits improved handling of faults by allowingback EMF to be controlled (by removing the field current).

A significant disadvantage to WFSMs is difficulty of couplingsignificant electrical power to a rotating rotor coil. Such coupling maybe done by using electrical “slip rings” in which brushes, typically acarbon composite material, mechanically slide on continuous orsemi-continuous metal rings. This mechanical approach is subject toproblems of wear on the brushes and rings and the problem of generatingdebris from such, which may contaminate the environment of the motor.

An alternative approach to mechanical electrical coupling is thetransfer of electrical energy by mutual inductance between coils of arotary transformer. In such a transformer, a stationary primary coil maycommunicate, via magnetic fields, with a secondary coil mounted torotate with the rotor. The conductive coils of a rotary transformer andthe ferromagnetic components normally used to concentrate the magneticflux may substantially increase the weight and cost of the motor.

Capacitive coupling is known for low-power electrical data transfer, forexample, for transferring digital data from a rotating device. The useof capacitive coupling in motor applications, for example, by usingadjacent rotating and stationary capacitor plates, is hampered byrelatively small capacitance that can be obtained with practicaltolerances and the need for significantly greater amounts of power forpractical motor operation.

SUMMARY OF THE INVENTION

The present invention provides a wound-field synchronous machine inwhich power is transferred to the rotor via capacitive coupling. In oneembodiment, capacitive coupling is obtained between a rotating andstationary capacitor plate by allowing one plate to float on a cushionof flowing air, generated by the relative motion of the plates, in themanner of an air bearing. Small changes in plate separation incident tothe floating plate configuration may provide a measurement of thevelocity of the rotor and inclusion of a capacitance-altering feature onone of the plates may also provide information about the rotor position.

Specifically, the present invention provides a wound field electricalrotating machine having a rotor mounted for rotation about an axis andincluding at least one electrical coil having a coil axis with acomponent perpendicular to the axis, the electrical coil comprising aconductor having first and second conductor ends. An electricalrectifier unit is attached to the rotor, to rotate therewith, andelectrically connected with the first and second conductor ends, and afirst and second capacitor plate attached to rotate with the rotor andelectrically connected with the electrical rectifier unit. A third andfourth capacitor plate are mounted to a frame so as not to rotate withthe rotor and positioned for capacitive coupling with a respective firstand second capacitor plate wherein the first, second, third, and fourthcapacitor plates may transfer power between the electrical coil and thethird and fourth capacitor plate at a range of angular positions of therotor about the axis.

It is thus a feature of at least one embodiment of the invention toprovide a power coupling system for field-wound electrical rotatingmachines that avoids the mechanical wear problems of slip rings andbrushes without the cost expense and weight of rotary transformers.

The first and second capacitor plates may be separate plates attached toa rotor axle to extend in planes normal to the axis separated along theaxis and wherein the third and fourth capacitor plates are interleavedbetween the first and second capacitor plate.

It is thus a feature of at least one embodiment of the invention toprovide an arbitrary capacitor area for a given plate spacing toleranceby an interleaving configuration.

The wound field electrical rotating machine may further include a powergeneration circuit substantially fixed with respect to the frame, so asnot to rotate with the rotor, and connected with the third and fourthcapacitor plates to provide alternating current power to at least oneelectrical coil having a frequency in excess of 50 kHz.

It is thus a feature of at least one embodiment of the invention topermit limited area capacitors to provide sufficient power for motoroperations by employing high-frequency currents at which such capacitorshave lower impedance.

The power generation circuit provides at least one watt of electricalpower to the electrical coil.

It is thus a feature of at least one embodiment of the invention toprovide practically useful motor or generator applications usingcapacitive coupling.

The power generation circuit may provide for regulation of outputcurrent to the third and fourth capacitor plates to a predeterminedvalue.

It is thus a feature of at least one embodiment of the invention toprovide a power generation system that may accommodate minor variationsin capacitance of the couplers with reduced power fluctuation. As thecapacitance drops, the frequency provided by the power generation systemmay increase to compensate.

The wound field electrical rotating machine further includes aninductance in series with at least one of the third and fourth capacitorplates, where the power generation circuit tracks a resonant frequencyof a series resonant circuit including at least the inductance and aseries combination of a capacitance formed between the first and thirdcapacitive plate and second and fourth capacitive plate, and wherein thepower generation circuit adjusts the alternating current signal to matcha frequency of the resonant frequency.

It is thus a feature of at least one embodiment of the invention toprovide a power generation circuit which may operate in a narrow lowimpedance frequency range and accommodate slight shifts in thatfrequency range with mechanical or electrical changes in the couplingcircuit.

The power generation circuit may adjust the alternating current signalto match a frequency of the resonant frequency by tracking zerocrossings of the alternating current signal and changing a voltagepolarity of the alternating current signal at the zero crossings.

It is thus a feature of at least one embodiment of the invention toemploy well understood “soft switching” techniques to provide desiredfrequency tracking and/or high efficiency.

At least one given pair of the first and third capacitive plates andsecond and fourth capacitive plates, a given plate of the given pair maybe movably mounted to change a spacing with the other plate of givenpair so that the given plate may float on air cushion adjacent to theother plate.

It is thus a feature of at least one embodiment of the invention toprovide narrower separation between the capacitor plates and hencehigher capacitance values than might be ordinarily obtained with fixedmechanical tolerances.

A dielectric material may be affixed to one of the given plate or theother plate of the given pair.

It is thus a feature of at least one embodiment of the invention toincrease the capacitance between the plates and prevent shorting betweenthe plates at zero motor velocity.

The wound field electrical rotating machine may further include a springbiasing the given plate toward the other plate of the given pair.

It is thus a feature of at least one embodiment of the invention tocontrol the stiffness of the separation of the plates against the aircushion for improved capacitance and stability.

The first, second, third, and fourth capacitive plates may have pairwise configurations selected from the groups consisting of parallelplanar plates and concentric cylindrical plates.

It is thus a feature of at least one embodiment of the invention toprovide a coupling system that may be flexibly implemented in a varietyof topologies.

The first and second capacitive plates and third and fourth capacitiveplates may be different ones of an air bearing journal and air bearingshaft.

It is thus a feature of at least one embodiment of the invention toprovide capacitive coupling in an air bearing structure.

The wound field electrical rotating machine may further include acapacitance monitor measuring a capacitance between at least one pair ofcapacitive plates to provide an output signal indicating velocity of therotor.

It is thus a feature of at least one embodiment of the invention toprovide a simplified method of determining motor velocity without aseparate velocity sensor.

The wound field electrical rotating machine may further include fieldcurrent control changing an electrical signal providing a magnetic fieldin the wound field electrical rotating machine as a function of theoutput signal indicating velocity of the rotor.

It is thus a feature of at least one embodiment of the invention toprovide velocity-based control of the motor using a capacitance-derivedvelocity.

The wound field electrical rotating machine may alternatively or inaddition use the capacitance monitor to provide an output signalindicating a position of the rotor.

It is thus a feature of at least one embodiment of the invention toprovide a simplified method of determining rotor position.

The wound field electrical rotating machine may further include a fieldcurrent control changing an electrical signal providing a magnetic fieldin the wound field electrical rotating machine as a function of theoutput signal indicating position of the rotor.

It is thus an object of at least one embodiment of the invention toprovide motor control based on capacitance-derived position.

These particular features and advantages may apply to only someembodiments falling within the claims and thus do not define the scopeof the invention.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a simplified representation of the wound-field electricalmotor according to the present invention providing a wound field rotorcoil attached via two capacitive coupling units with drive electronicsfor providing high-frequency AC power through the capacitive couplingunits to the coil of the rotor;

FIG. 2 is a schematic block diagram of the motor and drive electronicsof FIG. 1, the drive electronics including a switching circuit andswitch signal generator connected to a capacitance monitor for providingposition and velocity signals;

FIG. 3 is a cross-section of one capacitive coupling unit of FIG. 1taken along line 3-3 of FIG. 1 showing relative axial movement andspring biasing of one plate supported with a first gap on a cushion ofair generated by the other plate and showing a dielectric layer attachedto the movable plate;

FIG. 4 is a figure similar to that of FIG. 3 in which a dielectric layeris placed on the axially movable plate and showing a second gap largerthan the first gap caused by greater relative velocity between theplates;

FIG. 5 is a figure similar to that of FIGS. 3 and 4 showing contact ofthe plates at start up of the motor before the cushion of air isdeveloped, at which time the plates are insulated from each other by thedielectric layer;

FIG. 6 is a cross-section taken along line 6-6 of FIG. 1 showing sideribs formed in the movable plate to provide for stiffness and lightweight;

FIG. 7 is a plot of capacitance of the capacitive couplers and frequencyof the AC power used for computing motor velocity;

FIG. 8 is a top plan view of one capacitive coupling unit incorporatinga capacitance-altering feature to provide a capacitance signalindicating rotor position shown in an associated graph;

FIG. 9 is an embodiment providing two capacitive coupling units with asingle planar disk;

FIGS. 10 a and 10 b are figures showing alternative configuration of thecapacitive coupling units operating on an outer cylindrical surface ofrotor mounted capacitor plates;

FIG. 11 is a fragmentary perspective view of an air bearing providingcapacitive coupling units operating on an inner cylindrical surface of aframe mounted capacitor plate;

FIGS. 12 and 13 are cross-sectional figures taken along line 12-12 ofFIG. 11 showing the capacitive coupling unit when the motor is at restand during rotation;

FIG. 14 is a figure similar to FIG. 1 showing a field-wound electricalgenerator according to of the present invention; and

FIG. 15 a figure similar to FIG. 5 showing a multiphase version of theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIG. 1, a wound field synchronous machine 10 configuredas a motor may include stationary stator windings 12 opposed across amotor axis 14 and generating a magnetic field crossing the motor axis14.

A rotor 17 is positioned between the stator windings 12, may providerotor coil 16 (only the rotor coil 16 shown for clarity) wound about anaxis generally perpendicular to the axis 14. For clarity, only a singleloop of the rotor coil 16 is shown however it will be understood thattypically the rotor coil will comprise many turns of a conductor such ascopper wire formed in one or more loops. Generally the rotor coil 16will be supported on additional structure of the rotor 17 which may beeither non-ferromagnetic or ferromagnetic to concentrate the magneticflux generated by the rotor coil 16.

The rotor 17 may turn about the axis 14 as attached to a shaft 18, thelatter supported for rotation about axis 14 on bearings (not shown), thelatter held in a motor housing 19. Electric current through the rotorcoil 16 will generate a magnetic field according to principles wellknown in the art, the magnetic field directed generally perpendicularlyto the motor axis 14 and rotating with rotation of the rotor coil 16.

As is generally understood in the art, the stator windings 12 may beenergized by a stator winding control unit 20 which controllablyswitches the direction of the field extending between stator windings 12to promote an angular torque on the rotor coil 16 causing rotation ofthe rotor 17 and the shaft 18. The switching of current through thestator windings 12 to this torque may be done “open loop” withoutknowledge of the state of the rotor 17, or by means of position orvelocity feedback in which the state of the rotor 17 is monitored as afeedback signal using a position or velocity sensor of conventionaldesign (not shown) or a position sensing technique of the presentinvention to be described below.

The conductors of the rotor coil 16 may attach to a rectifier assembly22 which provides a direct current to the rotor coil 16 from AC currentlines 24 a and 24 b providing inputs to the rectifier assembly 22. Therectifier assembly 22 may be, for example, a full-wave rectifieremploying solid-state diodes of conventional design and may be mountedto rotate with the rotor coil 16 on the shaft 18.

Each of AC current lines 24 a and 24 b may in turn connect to one of twocapacitive coupling units 25. The capacitive coupling units 25 each havea capacitive plate pair including a rotating plate 26 and the stationaryplate 28. In this embodiment, two rotating plates 26 a and 26 b areused, one for each capacitive coupling unit 25, and comprise aconductive disk mounted at its center on the shaft 18 to extendperpendicularly therefrom so that it may rotate about the axis 14 withthe rotor 17 in a plane perpendicular to the axis 14. The rotatingplates 26 a and 26 b are individually attached to different ones of theAC current line 24 a and 24 b.

The non-rotating plates 28 a and 28 b of each capacitive coupling unit25 may be, in this embodiment, flexible conductive strips having acantilevered plate portion 61 extending over a broad surface ofrespective rotating plates 26 a and 26 b along a tangent to the axis 14.The non-rotating plates 28 a and 28 b are closely spaced to therespective rotating plates 26 a and 26 b across a narrow gap to providean electrical capacitance therebetween.

The non-rotating plates 28 are attached in turn to drive electronics 30providing AC power to the non-rotating plates 28 which may then becapacitively coupled to the rotating plates 26 a and 26 b, rectified bythe rectifier assembly 22, and provided as a DC current to the rotorcoil 16. Generally, as will be described in more detail below, the driveelectronics 30 may include a solid-state frequency synthesizer 32 forgenerating the AC signals 34 from a DC source at a controllablefrequency. The drive electronics 30 may be associated with monitoringcircuitry 36 which may monitor the drive electronics 30 and/or the ACsignal 34 to deduce motor parameters such as velocity and rotorposition, as will be described below.

Referring now to FIG. 2, the frequency synthesizer 32 may comprise astandard H-bridge array of transistors 44 receiving a source of DC power40 filtered by filter capacitor 42 and operating to switch the polarityof application of the DC power to an output providing the AC signals 34.Other synthesizing circuits known in the art may also be used includinghalf bridges, push-pull stages, etc. In one embodiment, as will bedescribed in more detail below, the switching transistors 44 areoperated in a pulse width modulated fashion (with the transistors on oroff) to produce a pulsed voltage output of variable duty cycle,typically at a frequency in excess of 50 kHz or preferably in excess of100 kHz and possibly in the megahertz range. Standard antiparalleldiodes are provided for each transistor 44. It will be understood thatthe shown MOSFET transistors may be replaced with other solid statedevices such as IGBTs and the like.

The gates of the switching transistors 44 are controlled by a switchlogic circuit 46 as will be discussed below which may optionally receivea current signal 48 monitoring the current of the AC signals 34 and avoltage signal 50 monitoring the voltage of the AC signal 34. It will beunderstood the current sensing and voltage monitoring could be performedat a variety of other locations. For example, the current sensing couldoccur at the DC bus (in series with one of the lines spanned bycapacitor 42) and the voltage sensing may not be required in certaincircumstances or may be inferred from knowledge of the voltage of the DCbus and the switching pattern of the transistors 44.

Referring still to FIG. 2, electrical power from the AC signal 34 willbe transferred through the capacitive coupling units 25 to the rotor 17to be received by the rectifier assembly 22 and from the rectifierassembly 22 to the rotor coil 16 electrically represented by a coilinductance 16′ and coil resistance 16″. The rectifier assembly 22 mayconsist of four solid-state semiconductor diodes arranged in a full waverectifier configuration as is generally understood in the art to convertthe high frequency AC signal 34 to a DC voltage applied across the rotorcoil 16. It will be appreciated that other rectifier configurations mayalso be used including a halfway rectifier voltage doubler, currentdoubler or voltage multiplier (Cockroft-Walton circuit).

In one embodiment, an inductor 47 may be placed in series with thecapacitive coupling units 25 between the frequency synthesizer 32through one capacitive coupling unit 25 through the rotor coil 16 andback through the other capacitive coupling unit 25. This inductor 47, inseries with the series capacitances of the capacitive coupling units 25(formed by the capacitance between non-rotating plates 28 and respectiverotating plates 26) and possible residual impedance of the rotor coil16, presents a series resonance at which the impedance to current flowthrough the rotor coil 16 is minimized. The frequency of the frequencysynthesizer 32 is accordingly set to this series resonance frequency inorder to maximize energy transfer to the rotor coil 16 from the lowoutput impedance frequency synthesizer 32.

In setting the frequency of the AC signal 34 to the series resonantfrequency, the switch logic circuit 46 may vary the output frequency ofthe frequency synthesizer 32 to compensate for slight changes in theseries resonant frequency, for example because of changes in thecapacitance of the capacitive coupling units 25 with motor speed (aswill be discussed below) and/or changes in other elements withtemperature or time or as a function of manufacturing tolerance. Thistracking may be done in a variety of ways, for example by trackingchanges in the phase of the current with respect to the voltage of theAC signal 34 derived voltage signal 50 and current signal 48. In oneembodiment, however, this tracking is provided automatically by precise“soft switching” of the transistors 44 at zero current points in thewaveform of the AC signal 34 such as will tend to drive frequency of thefrequency synthesizer 32 according to the natural resonance of inductor47 and rotor 17. The switch logic circuit 46 may also control the dutycycle of the AC signal 34 to provide a substantial constant current flowto the stator coil 16 related to a desired control point.

Referring now to FIG. 3, in one embodiment, the non-rotating plates 28are attached to the housing 19 at proximal end 54 but include a flexingportion 58 or a hinge or other pivot point types known in the artallowing axial motion 60 (generally along axis 14) of a distal plateportion 61. This distal plate portion 61 will be generally parallel to acorresponding surface of the rotating plates 26 a and 26 b spaced fromthat surface along axis 14 by a gap 62 which defines the capacitor plateseparation. Movement of the distal plate portion 61 thus may change thegap 62.

Rotary motion 64 of a rotating plate 26 beneath the non-rotating plate28 draws air 66 into the gap 62 compressing that air to provide an airbearing between the rotating plates 26 a and 26 b and non-rotating plate28. In this way, the non-rotating plate 28 may float on a thin film ofair against a bias force 68 applied to the non-rotating plate 28, forexample, by the natural elasticity of the strip of the non-rotatingplate 28 or by a separate spring or the like. The bias force 68 may beadjusted to control the stiffness of the positioning of the non-rotatingplate 28 for the purpose of stability and the like as well as to controlthe absolute separation.

An upper surface of the rotating plate 26 opposite the non-rotatingplates 28 may be coated with a dielectric layer 70 such as Teflon® orother material that may provide for insulation between the non-rotatingplate 28 and the rotating plates 26 a and 26 b when the non-rotatingplate 28 is no longer supported by the layer of air 66, for example, asshown in FIG. 3. Ideally, the dielectric layer 70 will have a breakdownvoltage sufficient to prevent electrical direct current flow betweenplate 28 and rotating plates 26 a and 26 b when there is zero air gap 62and will provide some abrasion resistance. The dielectric layer 70 alsoincreases the capacitance for a given gap 62.

In some embodiments, a zero air gap is also permissible at zero rotorspeed, even without a dielectric layer. In this case variable frequencyac or even dc may be supplied, which is then directly conducted onto therotor.

Referring now to FIG. 4, in an alternative configuration the dielectriclayer 70 may be attached to the under surface of the non-rotating plate28. This configuration shows a greater separation between non-rotatingplate 28 and rotating plates 26 as may occur as the velocity of rotatingplates 26 increases.

Referring now to FIG. 6, in one embodiment the non-rotating plate 28 mayhave ribs 72, for example, formed as wings on either side of thenon-rotating plate 28 to provide for greater stiffness and preventundesirable longitudinal vibrations in the non-rotating plate 28.

Referring now to FIG. 7, the relationship between the speed of rotatingplates 26 and the gap 62 between the rotating plates 26 and non-rotatingplate 28 (shown, for example, in FIGS. 3 and 4) affects the capacitancebetween each non-rotating plate 28 and rotating plates 26 and thus theseries resonant frequency of the inductor 47 and capacitive couplingsunits 25 discussed above. At low velocities, non-rotating plate 28 androtating plates 26 a and 26 b are closer together forming a highercapacitance 80 whereas at high velocities, the separation of therotating plates 26 and non-rotating plates 28 increases forming lowercapacitances 82. Per the description of the frequency synthesizer 32above, higher capacitances 80 will also result in a lower frequency ofthe AC signal 34 where is lower capacitance 82 will result in a higherfrequency of the AC signal 34 allowing capacitance to be deduced fromdrive frequency. In this way, monitoring the capacitance directly or viathe frequency of the AC signal 34, by rotor position and velocitycircuit 52, may determine the velocity of the rotor 17. Rotor positionand velocity circuit 52 may produce an output signal 86 indicating thisvelocity.

Referring now to FIG. 8, optionally, a sector 88 of the surface of therotating plates 26 a and 26 b opposite the non-rotating plate 28 may betreated, for example by removal of conductive material in the sector 88or change in the dielectric material of the sector 88, to produce aperturbations 92 in capacitance value 90 monitored by the rotor positionand velocity circuit 52. These perturbations 92 in capacitance valuewill occur at regular periods τ which will be a function of the rotatingspeed of the rotor 17. The magnitude of τ may thus be used to reveal thevelocity of the rotor 17 but may also reveal absolute position of therotor 17 at the times of perturbations 92. This position information maybe output from rotor position and velocity circuit 52 as output signal94.

Referring again to FIG. 1, output signal 86 of velocity and outputsignal 94 of position may be provided to the stator winding controlcircuit 20 to change the stator field based on speed or position of therotor 17 according to methods well understood in the art, for example toprovide power factor control. Alternatively, or in addition the samesignals may be provided to the frequency synthesizer 32 to control thecurrent supplied to the rotor 17 and hence the field of the rotor coil16. In either of these cases amplitude and/or phase or current may beadjusted as a function of position or velocity.

Referring now to FIG. 9, in an alternative embodiment, a single rotatingplate 26 may provide the rotating plate 26 two non-rotating plates 28 aand 28 b of two capacitive coupling units 25. This configuration mayallow for more compact construction and employs two electricallyisolated conductive rings 100, 102 concentric about the axis 14 forexample separated electrically by an insulating portion 104. For examplethe conductive rings 100, 102 may be conductive layers on an insulatingdisk-shaped substrate. In addition, annular sector shaped non-rotatingplates 28 a and 29 b allow for increased capacitive coupling area.

Referring now to FIGS. 10 a and 10 b, it will be appreciated that thegeometry of the capacitive couplings may be implemented in a hoop formin which the function of the rotating plates 26 a and 26 b isimplemented by an outer cylindrical surface of a cylindrical tube 110attached concentrically to the shaft 18 where the plate portion 61 ofthe non-rotating plate 28 is given an arcuate form to conform generallywith the outer periphery of the cylindrical tube 110 to move radiallytoward and away from axis 14 as indicated by arrow 112.

Referring now to FIGS. 11, 12 and 13, in an alternative embodiment,rotating plates 26 a and 26 b may be implemented as a cylindricalbearing element axially aligned with and attached to shaft 18. An outercircumferential surface of the cylindrical bearing element may in turnbe surrounded by an inner cylindrical surface of a journal elementproviding non-rotating plates 28. The outer diameter of the rotatingplates 26 may be close to the inner diameter of non-rotating plates 28so that air 66 between the two provide for an air bearing actionsuspending the bearing element of the rotating plate 26 on a cushion ofair 66 within the journal element of the non-rotating plate 28 duringrotary motion 114 of the shaft 18. As before, a dielectric layer 70 maybe applied to the outer surface of the rotating plates 26 a and 26 b (asshown) or the inner surface of the stator capacitive rotating plates 26to accommodate contact between the two when there is no rotation.

Referring now to FIG. 12, it will be appreciated that theabove-described principles may also be used with respect to a woundfield synchronous machine 10 configured as generator 120 in which amagnetic field is established on a rotor coil 16 through a rectifierassembly 22 which receives an AC signal 34 through capacitive couplingunits 25 from drive electronics 30. In this case, the stator windings 12may be attached to drive a load 122.

It will further be appreciated that multiple pairs of non-rotatingplates 28 and rotating plates 26 may be combined for each capacitivecoupling unit 25 (in any of the configurations described herein) to gainthe benefits of parallel addition of their capacitances. It will befurther appreciated that the configuration of the non-rotating plates 28may be exchanged with the configuration of the rotating plates 26, as itis their relative motion rather than their absolute motion which is ofprincipal significance. It should be apparent that “capacitor plate” asused herein will be understood is not limited to planar plates but maybe of any configuration in which a gap may be maintained with rotationof the corresponding plates of a capacitor.

Referring now to FIG. 15, it will be appreciated that the principles ofthe present invention may be extended to multiphase motor/generatorconfigurations. In this case, the frequency synthesizer may producen-phase power where n is an integer (for example, three phase power asshown providing three approximations to sine waves each having relativephase shifts of 120 degrees with respect to the others). In this case ofthree-phase power, three inductors 47, 47′, 47″ may be placed in serieswith each of the three capacitive coupling units 25 (one associated witheach phase) to provide the necessary resonant operation. The rectifierassembly 22 is likewise modified to handle three phase rectification.This approach provides reduced field current ripple and can be readilyextended to any number of phases.

Certain terminology is used herein for purposes of reference only, andthus is not intended to be limiting. For example, terms such as “upper”,“lower”, “above”, and “below” refer to directions in the drawings towhich reference is made. Terms such as “front”, “back”, “rear”, “bottom”and “side”, describe the orientation of portions of the component withina consistent but arbitrary frame of reference which is made clear byreference to the text and the associated drawings describing thecomponent under discussion. Such terminology may include the wordsspecifically mentioned above, derivatives thereof, and words of similarimport. Similarly, the terms “first”, “second” and other such numericalterms referring to structures do not imply a sequence or order unlessclearly indicated by the context.

It will be appreciated from the above discussion that although separatecapacitive coupling units 25 are described for providing power to andreceiving power from the rotor 17, it may be possible to employparasitic capacitances 123 (shown in FIG. 14) existing naturally betweenstructures of the motor or generator (for example from the statorwinding 12 to the housing 19) for one of these functions and thus torequire as little as one capacitive coupling unit 25.

When introducing elements or features of the present disclosure and theexemplary embodiments, the articles “a”, “an”, “the” and “said” areintended to mean that there are one or more of such elements orfeatures. The terms “comprising”, “including” and “having” are intendedto be inclusive and mean that there may be additional elements orfeatures other than those specifically noted. It is further to beunderstood that the method steps, processes, and operations describedherein are not to be construed as necessarily requiring theirperformance in the particular order discussed or illustrated, unlessspecifically identified as an order of performance. It is also to beunderstood that additional or alternative steps may be employed.

References to “a controller” and “a processor” can be understood toinclude one or more controllers or processors that can communicate in astand-alone and/or a distributed environment(s), and can thus beconfigured to communicate via wired or wireless communications withother processors, where such one or more processor can be configured tooperate on one or more processor-controlled devices that can be similaror different devices. Furthermore, references to memory, unlessotherwise specified, can include one or more processor-readable andaccessible memory elements and/or components that can be internal to theprocessor-controlled device, external to the processor-controlleddevice, and can be accessed via a wired or wireless network.

It is specifically intended that the present invention not be limited tothe embodiments and illustrations contained herein and the claims shouldbe understood to include modified forms of those embodiments includingportions of the embodiments and combinations of elements of differentembodiments as come within the scope of the following claims. All of thepublications described herein, including patents and non-patentpublications, are hereby incorporated herein by reference in theirentireties.

We claim:
 1. A wound field electrical rotating machine comprising: arotor mounted for rotation about an axis and including at least oneelectrical coil having a coil axis with a component perpendicular to theaxis, the electrical coil comprising a conductor having first and secondconductor ends; an electrical rectifier unit attached to the rotor torotate therewith and electrically communicating with the first andsecond conductor ends; at least one first capacitor plate attached torotate with the rotor and electrically communicating with the electricalrectifier unit; at least one second capacitor plate mounted to a frameso as not to rotate with the rotor and positioned for capacitivecoupling with the first capacitor plate; wherein the first and secondcapacitor plates are positioned to transfer power to the electrical coilat a range of angular positions of the rotor about the axis.
 2. Therotating machine of claim 1 further including a third capacitor plateattached to rotate with the rotor and electrically communicating withthe electrical rectifier unit and a fourth capacitor plate mounted to aframe so as not to rotate with the rotor and positioned for capacitivecoupling with a respective first and second capacitor plate wherein thethird and fourth capacitor plates are positioned to return power fromthe electrical coil at a range of angular positions of the rotor aboutthe axis.
 3. The rotating machine of claim 2 wherein the first and thirdcapacitor plates are separate plates attached to a rotor axle to extendin planes normal to the axis separated along the axis and wherein thesecond and fourth capacitor plates are interleaved between the first andsecond capacitor plates.
 4. The rotating machine of claim 1 furtherincluding a power generation circuit substantially fixed with respect tothe frame so as not to rotate with the rotor and communicating with thesecond and fourth capacitor plates to provide alternating current powerto the at least one electrical coil having a frequency in excess of 50kHz.
 5. The rotating machine of claim 4 wherein the power generationcircuit provides at least one watt of electrical power to the electricalcoil.
 6. The rotating machine of claim 4 wherein the power generationcircuit provides for regulation of output current to the second andfourth capacitor plates to a predetermined value.
 7. The rotatingmachine of claim 4 further including an inductance in series with atleast one of the capacitor plates wherein the power generation circuittracks a resonant frequency of a series resonant circuit, including atleast the inductance, and a series combination of a capacitance formedbetween the first and second capacitive plate, and between the third andfourth capacitive plate, and wherein the power generation circuitadjusts the alternating current power to match a frequency of theresonant frequency.
 8. The rotating machine of claim 7 wherein the powergeneration circuit adjusts the alternating current signal to match afrequency of the resonant frequency by changing a voltage polarity ofthe alternating current signal at the zero crossings of the currentsignal.
 9. The rotating machine of claim 1 wherein for at least onegiven pair of the first and second capacitive plates, as a pair, andthird and fourth capacitive plates, as a pair, a given plate of thegiven pair is movably mounted to change a spacing with the other plateof the given pair so that the given plate may float on an air cushionadjacent to the other plate of the given pair.
 10. The rotating machineof claim 9 including a dielectric material attached to one of the givenplates and the other plate of the given pair.
 11. The rotating machineof claim 9 further including a spring biasing of the given plate towardthe other plate of the given pair.
 12. The rotating machine of claim 9wherein the associated first, second, third, and fourth capacitiveplates have pair wise configurations selected from the groups consistingof parallel planar plates and concentric cylindrical plates.
 13. Therotating machine of claim 9 wherein the first and third capacitiveplates, as a pair, and second and fourth capacitive plates, as a pair,define an air bearing journal and air bearing shaft.
 14. The rotatingmachine of claim 9 further including a capacitance monitor measuring acapacitance between the given pair to provide an output signalindicating velocity of the rotor.
 15. The rotating machine of claim 14further including a field current control changing an electrical signalproviding a magnetic field in the rotating machine as a function of theoutput signal indicating velocity of the rotor.
 16. The rotating machineof claim 9 further including a capacitance monitor measuring acapacitance between the given pair to provide an output signalindicating a position of the rotor.
 17. The rotating machine of claim 16further including a field current control changing an electrical signalproviding a magnetic field in the rotating machine as a function of theoutput signal indicating position of the rotor.
 18. A method ofoperating a wound field electrical rotating machine having a rotormounted for rotation about an axis and including at least one electricalcoil having a coil axis with a component perpendicular to the axis, theelectrical coil comprising a conductor having first and second conductorends and further having an electrical rectifier unit attached to therotor to rotate therewith and electrically communicating with the firstand second conductor ends, and with a first and second capacitor plateattached to rotate with the rotor and electrically communicating withelectrical rectifier unit and a third and fourth capacitor plate mountedto a frame so as not to rotate with the rotor and positioned forcapacitive coupling with a respective first and second capacitor plate,the method comprising the step of: applying an alternating voltageacross the third and fourth capacitor plate to induce current flow inthe electrical coil to cause continuous rotation of the rotor bycapacitive coupling between the first and third and between the secondand fourth capacitor plates over a range of angular positions of therotor about the axis.